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.\" $FreeBSD: src/lib/libc/gen/ucontext.3,v 1.3 2004/07/03 22:30:08 ru Exp $
.\"
.Dd September 10, 2002
.Dt UCONTEXT 3
.Os
.Sh NAME
.Nm ucontext
.Nd user thread context
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In ucontext.h
.Sh DESCRIPTION
The
.Vt ucontext_t
type is a structure type suitable for holding the context for a user
thread of execution.
A thread's context includes its stack, saved registers, and list of
blocked signals.
.Pp
The
.Vt ucontext_t
structure contains at least these fields:
.Pp
.Bl -tag -width ".Va mcontext_t\ \ uc_mcontext" -offset 3n -compact
.It Va "ucontext_t *uc_link"
context to assume when this one returns
.It Va "sigset_t uc_sigmask"
signals being blocked
.It Va "stack_t uc_stack"
stack area
.It Va "mcontext_t uc_mcontext"
saved registers
.El
.Pp
The
.Va uc_link
field points to the context to resume when this context's entry point
function returns.
If
.Va uc_link
is equal to
.Dv NULL ,
then the process exits when this context returns.
.Pp
The
.Va uc_mcontext
field is machine-dependent and should be treated as opaque by
portable applications.
.Pp
The following functions are defined to manipulate
.Vt ucontext_t
structures:
.Pp
.Bl -item -offset 3n -compact
.It
.Ft int
.Fn getcontext "ucontext_t *" ;
.It
.Ft int
.Fn setcontext "const ucontext_t *" ;
.It
.Ft void
.Fn makecontext "ucontext_t *" "void \*[lp]*\*[rp]\*[lp]void\*[rp]" int ... ;
.It
.Ft int
.Fn swapcontext "ucontext_t *" "const ucontext_t *" ;
.El
.Sh SEE ALSO
.Xr sigaltstack 2 ,
.Xr getcontext 3 ,
.Xr makecontext 3
